An office machine such as a multifunction peripheral and an image scanning apparatus becomes an essential electronic device in the office. For continuously feeding a stack of documents to increase the scanning speed, the multifunction peripheral and the image scanning apparatus usually has an automatic document feeder. As the scanning speed is gradually increased, the speed of feeding sheets needs to be correspondingly increased. Since the sheet feeding speed becomes fast, excessive shock and noise are generated during the process of feeding the sheets. In this situation, the useful life of the automatic document feeder is shortened.
FIG. 1 is a schematic view illustrating an automatic document feeder disclosed in U.S. Pat. No. 6,792,241. As shown in FIG. 1, the automatic document feeder 1 comprises a sheet pick-up arm 10, a sheet pick-up roller 11, a sheet separation pad 12 and a sheet separation roller 13.
The sheet pick-up arm 10 of the automatic document feeder 1 is used for feeding the sheets S into the inner portion of the automatic document feeder 1. Depending on different sheet-feeding statuses, the sheet pick-up arm 10 may be switched between a standby position and a sheet feeding position. As shown in FIG. 1, the sheet pick-up arm 10 is in the standby position.
FIG. 2 is a schematic view illustrating the automatic document feeder of FIG. 1, in which the sheet pick-up arm is in a sheet feeding position. When the scanning operation is activated, the sheet pick-up arm 10 is lowered to the sheet feeding position. As such, the sheets S will be successively fed into the sheet feeding path D through a feeding entrance C by the sheet pick-up roller 11. Correspondingly, the sheets S are successively separated from and transported into the inner portion of the automatic document feeder 1.
The conventional automatic document feeder 1, however, still has some drawbacks. As previously described, the sheet pick-up arm 10 of the automatic document feeder 1 should be switched from the standby position to the sheet feeding position in order to feed sheets. For further increasing the sheet feeding speed, the office machine having the automatic document feeder needs to increase the speed of rotating the sheet pick-up arm 10 from the standby position to the sheet feeding position. As such, the striking force applied on the feeding entrance C by the pick-up arm 10 becomes stronger, and excessive shock and noise are generated. In this situation, the use life of the sheet pick-up arm 10 is shortened. Therefore, there is a need of an automatic document feeder with reduced shock and noise during the process of feeding sheets by the sheet pick-up arm in order to obviate the drawbacks encountered from the prior art.